1. Field of the Invention
The present invention relates to a modified combustion engine for burning particulate fuel, such as corn starch or other suitable renewable energy source and a method for operating same. The invention includes a fuel feed system which delivers the powdered or particulate fuel to a mix chamber where it is mixed with previously dried and compressed air. The fuel mixture is then delivered to the combustion chamber of a valve where it undergoes expansion, compression and then deflagration to power the combustion engine.
2. Description of the Related Art
It is long been known that fine solid particles, such as flour, can be a very volatile material under the proper conditions. The National Fire Protection Agency has established a volatility value to most common particulate fuels or dusts in the form of a Kst rating which is a deflagration index for dusts and is expressed as bars/millisecond. If methane is compared to corn starch under detonation conditions, the corn starch produces three times the energy force of the methane gas per unit volume. It has long been recognized that solid fuels are a more effective fuel source than gas which is why rockets are powered by solid fuel cells.
There are four factors that are needed to produce an explosion, whether in the combustion chamber of an engine or any other enclosure. They are a fuel source, an oxidant, a containment area, and an ignition source. In a simple combustion engine, the fuel source is vaporized liquid gasoline, the oxidant is air, the cylinder is the containment area, and the spark plug is the ignition source. The cylinder containment area is created collectively by the cylinder wall, the piston and cylinder head.
On the down stroke of the piston the inlet valve opens and allows the fuel and air mixture to enter the combustion chamber. As the piston returns to the top position, the inlet valve closes and the mixture is compressed. When the piston reaches the top of the stroke, the spark plug detonates the fuel causing the piston to be driven to the down position, turning a crank shaft and producing work force which has the discharge valves vent gas from the combustion chamber.
The combustion engine only requires the fuel source to produce the required energy to drive the shaft work force requirements and that the fuel burns fully and does not coat the valves, cylinder head or cylinder walls. Certain dusts or particulate fuel would burn cleanly and would produce very high energy levels when burned as fuel in a combustion engine. These particulate fuels would include cornstarch, soy flour, sucrose, coffee and wheat. Chemical particulate fuel such as ethylene diamine, ortazol, coal, charcoal and sodium lignosulfate would also be good fuel sources.
A standard combustion engine would, of course, require modifications to use dust fuel and to overcome challenges of burning fuels that the engine was not designed to burn. The first major challenge or modification that would be needed in a standard combustion engine would be in the delivery system of the fuel and air mixture to the combustion chamber.
The second major challenge or modification that would be needed would be in the means to control the increased heating of the combustion chamber. In a standard combustion engine, vaporized gasoline provides cooling to the combustion chamber during the down stroke of the piston. To offset this lost cooling, the particulate fuel mixture should be delivered at a pressure of 25 psig or greater to the combustion chamber where it will be allowed to expand. This expansion will cause a Joule-Thomson effect or a refrigeration effect due to the decrease in pressure of the fuel mixture as is moves from the storage system to the combustion chamber.
Under normal conditions, the fuel to air ratio would be between approximately 1-2 percent particulate fuel and between 98-99 percent compressed air. The mixing system must be able to suspend the particulate fuel particles in the air mixture until the spark is delivered to the combustion chamber. During acceleration, the engine would require more power and the fuel to air ratio would increase to as much as 5-7 percent particulate fuel and 93-95 percent air. This makes the engine very efficient. It is estimated that a four cylinder car could travel 100 miles at 65 miles an hour on a single pound of particulate cornstarch fuel. Because of the very low LFL (lower flame level) or low ignition point of cornstarch, there would be nearly complete burning of the fuel, with very little material to collect on the moving surfaces of the combustion chamber or valves. This clean burning fuel would eliminate most waste bi-products from the engine exhaust.
Particulate fuel is a truly renewable fuel source that requires very little refining and processing. The fuel is readily available and safe to store and transport because it is only volatile once the four elements required for detonation are present, i.e. fuel, oxidizer, containment, and ignition. The use of particulate fuel as a fuel source could be expanded to use in heating homes, in producing electricity and in space travel. The knowledge and technology for such uses is available now.
The term “detonation” means a loud, violent explosion. Thus detonation is not desirable in a combustion engine. Detonation can cause major damage to an engine. The proper term for the method of combustion would be “deflagration” which is burning fuel at a rate below sonic velocity. Deflagration is the desired type of combustion of the present invention. By controlling the fuel mixture and limiting the size of the combustion chamber, detonation would be unlikely under normal conditions for a combustion engine of the present invention. It is also important to control the size of the particulate fuel particle to achieve uniform and clean burning. The smaller the particulate fuel particle, the faster the deflagration occurs. Thus it is important that the fuel be reduced to the proper particle size before use in the present invention. A particle size of between 8-12 microns is preferred.
It is also important in the engine of the present invention to control the quality of the incoming air. If the air contains too much moisture, the fuel mixture will burn too slowly or will not burn at all and will not produce the discharge energy required. By feeding the inlet air through desiccant dryers, a moisture level in the combustion air can be maintained at a minimum level of −10 degrees pressure dew point. To achieve this level of moisture reduction in the combustion air, the system would use two dryers. One dryer would provide combustion air to the compressor, while the second dryer would be purging the water vapor it had collected. The purging dryer would be under a slight vacuum produced by a venturi created in association with the exhaust stack of the engine. The dryers would alternate every few minutes so that a fresh purging dryer would always be supplying the dried air to the mixing chamber where the air would be mixed with the fuel.
To increase lubrication to the cylinder wall, a small amount of graphite particles could be added to the fuel mixture. It is believed that a graphite level of 0.01 percent would not retard the combustion rate and would provide the needed lubrication.
Because the present engine uses renewable resources as its fuel source, it can offer an endless source of clean, efficient energy for many generations to come.
Although some prior art patents suggest the desirability of burning renewable fuels, the prior art patents do not address how the fuel would be delivered to the combustion chamber so that the engine operates efficiently on these fuels, i.e. preparing the fuel to the proper particle size and moisture content and mixing or atomizing it with oxidant. Operating an internal combustion or turbine on organic particles requires a high degree of control of the fuel which is not taught in the prior art. If moisture is not adequately controlled, the engine might only function when the relative humidity is very low. If the fuel to air ratio is not proper, then there is incomplete burning or there is detonation.
Another key component to a successful organic fuel-burning engine is to maintain and control the burning speed of the fuel. The engine must operate under “deflagration” conditions. If burning speed exceeds subsonic velocity, then detonation occurs which will severally damage the engine. There are five elements that must be controlled in order to control the burning speed of the fuel. These elements are particle size of the fuel, pressure dew point of the combustion air, fuel to air mixture ratio, containment area, and ignition source. The present invention controls all five elements for successful operation.
The pre-burn preparation of the fuel and the pre-ignition mixing of the proper fuel to air ratio of the fuel and air mixture that enters the combustion chamber are mandatory for successful operation of a particulate combustion engine. The prior art attempts to combine the particulate fuel and air in the combustion chamber and this leads to incomplete mixing and failure to achieve the crucial uniform particle suspension of the fuel mixture prior to combustion. If particle suspension does not occur before combustion, then only a portion of the fuel will be burned. The unspent or unburned fuel will then coat the combustion chamber and greatly damage the engine, resulting in further reduction in engine performance and a greater likelihood of detonation of the fuel.
The present invention pre-mixes the fuel air ratio before it enters the combustion chamber. The invention employs an infrared sensor that monitors the combustion chamber for fuel density and flame speed of the deflagration before and during the combustion phase. If the burn speed nears sonic velocity the fuel mixture ratio changes to retard the burn speed. This system allows for total consumption of the fuel and prevents unburned fuel from damaging the engine. Oxygen and dew point sensors insure that the combustion air quality entering the pre-combustion mixing chamber remains within the proper range.
Obviously, because each fuel has a different Kst value, the delivery system would need to be adjusted for a new fuel should the type of fuel employed in the invention be changed.